Host-graft circulation and vascular morphology in pancreatic tissue transplants in rats

One of the most determining factors for the survival of tissue grafts is an intact vasculature. This vasculature must, however, be linked to the circulation of the host animals for survival and growth to occur. The mechanism(s) of revascularization of pancreatic tissue grafts is still unclear and more so the process by which the host blood vessels anastomose with those of the graft. The microvasculature and revascularization of neonatal pancreatic tissue fragments transplanted into the anterior eye chamber of rats were investigated using conventional light and electron microscopy as well as the india ink perfusion method. Light microscopy demonstrated that the blood vessels of the host iris revascularized the transplants within 24 h of transplantation. Sinusoidal blood capillaries were observed to invade the peripheral parts of the grafts. The capillary encroachment from the iris into the graft continued through the second day of transplantation. The host-graft anastomosis developed completely and became prominent and conspicuous after the third day of transplantation. Many capillaries were observed to encroach into the graft from the iris. The vasculature of the graft was increased in comparison with that of normal pancreatic tissue. This increase was prominent especially around pancreatic islet and ductal cells which survived after transplantation. Blood cells observed in these vessels of the graft indicated a functional state. The ultrastructure of the intrinsic blood vessels of the graft was intact and showed the peculiar fenestrations normally seen in the blood vessels of endocrine tissues. These observations indicated that pancreatic tissue fragments transplanted into the anterior eye chamber of rats were revascularized within 24 h. The revascularization was completed at the end of the third day of transplantation when definitive blood vessels linked the circulation of the graft with that of the iris.